1. Technical Field
The present invention relates to a system for controlling air intake for an automotive engine and more particularly, to an improvement of controlling air intake for an horizontally-opposed type engine or a V-shaped engine which has two banks, i.e., a left-hand bank and a right-hand bank to provide two intake systems.
2. Description of the Relates Art
In recent years, an engine mounted on a vehicle is equipped in its intake system with an apparatus for controlling an air intake in order to assure that a high intake efficiency is maintained in a wide range from a lower speed range to a higher speed range. With such an apparatus, an intake inertia effect and a swirl effect are created by using a small diameter and long intake passage when the engine is operated at a low or intermediate speed with a small quantity of the intake air induced thereinto, whereby an intake efficiency and a combustion characteristic are improved. When the engine is operated at a high speed, the apparatus operates to feed a large quantity of air by a large diameter and short intake passage which has reduced resistance against air introduction so that an engine output is increased. To fully achieve an advantageous effect of the apparatus, the latter is often employed for a two intake valve type engine.
With respect to the former type of the apparatus for variably controlling the air intake, a typical one is disclosed in Japanese Laid-Open Pat. No. 224,933/1985 which is incorporated therein for reference. The apparatus includes two intake ports which are communicated with high speed intake passages and another intake port which is communicated with a low speed intake passage. Each of the high speed intake passages is provided with a valve at a position located in the proximity of the intake port so as to allow it to be closed in a low rotational speed range and opened in a high rotational speed range with controlling means.
With the conventional apparatus as mentioned above, the valves for the high speed intake passages are arranged near to an engine housing. Accordingly, it is preferable for a vertical type engine but it is not suitable for a horizontally opposed type engine. In case of the horizontally opposed type engine, a cylinder head is designed to have two banks which are a left-hand bank and a right-hand bank. This gives a rise for attaching an actuator to each bank when the valves are disposed in the same manner as the prior art. In case where the apparatus is operated by a single actuator, it is necessary that the valves on both the banks are operatively connected to each other using a long rod, cable or the like. This causes the apparatus to become complicated in structure. Moreover, it becomes difficult to operate the apparatus smoothly.
Other problems with the conventional apparatus are that when the engine is operated in the low or intermediate rotational speed range with the valves in the high speed intake passages kept closed, a more quantity of air is induced into one intake port via the low speed intake passage while the other intake port is fed with less quantity of air, and a volumetric efficiency is reduced due to a resistance against air induction in the flow passage.
Further, another problem is that torque decreases when the valves in the high speed intake passages are opened at the high rotational speed. In this case, a characteristic curve representative of variation of an engine torque does not show a smooth one.